1. Field of the Invention
The present invention relates to an electrolytic capacitor and a method of manufacturing an electrolytic capacitor.
2. Description of the Background Art
In recent years, an electric circuit has been required to have a smaller size and to adapt to high frequency, and accordingly, a capacitor is also required to have low impedance or the like. Then, an electrolytic capacitor including TCNQ complex salt or a conductive polymer such as polypyrrole, polythiophene, polyfuran, and polyaniline as a solid electrolyte of the capacitor has attracted attention.
FIG. 3 is a perspective view schematically showing a wound-type capacitor element in a conventional electrolytic capacitor. FIG. 4 is a cross-sectional view of the conventional electrolytic capacitor. A structure or the like of the conventional electrolytic capacitor is disclosed, for example, in Japanese Patent Laying-Open No. 2003-217979. A method of manufacturing the conventional wound-type electrolytic capacitor including a solid electrolyte will be described with reference to FIGS. 3 and 4.
Initially, an anode foil 22 subjected to etching process, chemical conversion treatment and the like by using a known method is prepared. Then, an anode lead 27 is attached to anode foil 22 through a lead tab terminal 26. Thereafter, a cathode lead 28 is attached to a cathode foil 23 through lead tab terminal 26. Then, an anode foil 22 and cathode foil 23 are wound up with a sheet of separator paper 24 being interposed therebetween and taped with a stop tape 25. Through the steps above, a wound-type capacitor element including a winding structure portion 21 formed of a wound-type layered structure and an anode terminal consisting of lead tab terminal 26 and anode lead 27 and a cathode terminal consisting of lead tab terminal 26 and cathode lead 28 is formed.
Thereafter, winding structure portion 21 is subjected to chemical conversion treatment of a cut section and heat treatment at a temperature from 150° C. to 300° C. Then, winding structure portion 21 is impregnated with a solution mixture of a monomer forming a conductive polymer through polymerization and an oxidizing agent solution such as a ferric p-toluenesulfonate alcohol solution. Thereafter, through thermochemical polymerization, a conductive polymer layer serving as a solid electrolyte can be formed between anode foil 22 and cathode foil 23 of winding structure portion 21.
Then, the wound-type capacitor element including the solid electrolyte is accommodated in a bottomed case 29 made of aluminum. Then, a sealing member 30 for sealing winding structure portion 21 within bottomed case 29 is placed in an opening of bottomed case 29. Thereafter, the wound-type capacitor is sealed by performing pressing in a lateral direction and curling in the opening of bottomed case 29, and aging treatment is performed.
Finally, a seat plate 31 made of plastic is provided on a curled surface around the opening of bottomed case 29 and anode lead 27 and cathode lead 28 are pressed and bent as electrode terminals 32, to complete the electrolytic capacitor.
Thermal stress, however, is applied to the wound-type electrolytic capacitor element during heat treatment or the like in the process of manufacturing such an electrolytic capacitor, and consequently, lower density of separator paper 24 is caused. In addition, mechanical stress is applied to the wound-type electrolytic capacitor element in such treatment as solid electrolyte filling in the manufacturing process, and consequently the electrolytic capacitor element may expand or deform. Then, positions of the anode terminal and the cathode terminal of the wound-type electrolytic capacitor element may be displaced from a desired position due to thermal stress and mechanical stress.
Moreover, in assembling the electrolytic capacitor, if sealing member 30 is forcibly placed after the wound-type capacitor element is accommodated in bottomed case 29, positions of the anode terminal and the cathode terminal may be displaced. In particular, if the sum of the number of anode terminals and the number of cathode terminals is not smaller than three, slight displacement of the anode terminal and the cathode terminal hinders placement of the sealing member of the electrolytic capacitor. Then, stress is applied to the anode foil and the cathode foil, which may result in increase in a leakage current or the like.